Inductorless controlled transition and other light dimmers

ABSTRACT

A light dimmer, especially useful for entertainment lighting, provides a high degree of stability in dimmer performance by employing a high level of analog negative feedback and correcting for the undesirable effects on dimmer &#34;curve&#34; by precompensating the input value while it is digital. A lighting control system distributes both the alternating current supply and control signals representing desired adjustments to fixture intensity via a housing common to multiple enclosures. Each enclosure contains at least one dimmer and mechanically engages the housing, from which it obtains a power input via power contacts and a control signal via an electrically isolated coupling comprising an effective source on the housing and detector on the enclosure.

This application relates to lighting control, and more specifically tocontrolled transition light dimming apparatus. It represents acontinuation of application Ser. No. 07/615,517, filed Nov. 19, 1990,now abandoned, which is a continuation of application Ser. No.07/336,014, filed Apr. 10, 1989, now U.S. Pat. No. 4,975, 629, which isa continuation-in-part of application Ser. No. 06/943,381, filed Dec.17, 1986, now U.S. Pat. No. 4,823,069, which is a continuation-in-partof application Ser. No. 06/640,978, filed Aug. 15, 1984, now U.S. Pat.No. 4,633,161, included in their entirety by reference, and containsadditional material in Disclosure Documents Nos. 213,965, 213,971,215,867 and 215,941.

Prior related applications disclose various improvements to lightdimmers, especially those used for entertainment lighting applications.Some of these improvements are to phase control dimmers directlycontrolling the duration of the transition of the semiconductor powercontrolling means between one and the other of its substantiallyconductive and substantially non-conductive conditions so as to limitEMI without the need for a conventional choke. Other improvements areapplicable to the design of lamp dimmers of both the controlledtransition and more conventional types, particularly those fordistributed applications.

The present application discloses several such improvements addressingprior difficulties with the design of such lamp dimmers.

One improvement relates to an improved triggering circuit for lampdimmers. It is well known that variations in the alternating currentsupply, the components of the dimmer itself, and in the impedance of theconnected load may result in undesirable variations relative to thedesired value as expressed by the value supplied to the dimmer's controlinput, in the actual average power supplied to the lamp load (andtherefore in lamp brightness). Analog voltage feedback was long employedto correct for such variations, but, in addition to requiring voltageisolation of the sense input to the triggering stage from the dimmer'soutput, resulted in triggering circuits difficult to design well, lessthan stable in performance, and requiring regular trimming. Suchdisadvantages have become still more acute with the transition todimmer-per-circuit systems, and a simple and reliable alternative haslong been sought, particularly for applications in which one triggeringstage is required for each power stage. The present applicationdiscloses a "precision analog dimmer" which employs previouslyundesirably high levels of analog feedback to achieve the requiredstability, while precompensating the control input value while still inthe digital domain to correct for the otherwise unacceptable effect ofthe dimmer's high level of feedback on its "curve". The result is auniquely simple and inexpensive triggering circuit offering manyadvantages.

Another disadvantage of prior art triggering circuits sensing actualline voltage, whether for analog feedback or for input to amicroprocessor, is the requirement for voltage isolation between linevoltage and the triggering circuit. In professional dimmers of the past,the control signals supplied to the input to the triggering circuit areat low voltages, and therefore the triggering stage must be operated atsimilar voltages. This requires isolation of the triggering circuit fromline voltage by means of transformers for both power supply and toprovide voltage feedback for regulation purposes from the dimmer'soutput to the triggering stage. Such transformers are relatively largeand expensive, and suitable alternatives have been long andunsuccessfully sought. The present application discloses the use of avoltage isolation means, such as an opto-isolator, at the digital inputto the triggering stage. Such isolation at this point is of minimal costand has no effect on the performance of the dimmer, but allows thetriggering card to operate at any voltage, such that the triggering cardcan derive voltage feedback (and power supply) without the need fortransformers. Further, where the dimmer is constructed as a mechanicalmodule that accepts its control input via a mechanical structure thatdistributes signals and power to a plurality of such dimmers/modules,the voltage isolation means at the control input can be located acrossthe mechanical interface between the module and the structure such thatsaid isolation means also serves the function of an interconnect betweenthe two, with unique advantages. Where the two halves of the voltageisolation means require alignment with each other, the same means usedto mechanically align the module and the structure, especially formating of power contacts, can align the isolation means. For thispurpose, the isolation means may be made integral with the power contactassembly. Further, the function of the control input need not be limitedto the transmission of dimmer values. Where the modular dimmer islocated in proximity to the lamp, the means used to distribute controlsignals to the dimmer may be used to distribute control signals foraccessories (such as a color-changer) used with the same fixture, andthe dimmer module may incorporate means to supply that accessory withits control signals.

Various methods suitable for separately addressing dimmer modules and ofsimplifying the distribution of data to them, applicable to bothcentralized modular racks and fully distributed systems are alsodisclosed.

Other features and advantages of the disclosed improvements will becomeapparent.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a controlled transition dimmer.

FIG. 1B is a block diagram of a controlled transition dimmer adapted forthe use of power devices with an input voltage/output currentrelationship. FIG. 1C is a block diagram of a controlled transitiondimmer with several improvements.

FIG. 1E is an output waveform typical of a conventional phase-controldimmer.

FIG. 1F is an output waveform of a phase-control dimmer with atransition in every other half-cycle.

FIG. 1G is an output waveform of a phase-control dimmer producingdesired average power by averaging different firing angles in twohalf-cycles.

FIG. 1H is an output waveform of a phase-control dimmer producingdesired average power by the use of the techniques of the previousFigures.

FIG. 1I is a symmetrical output waveform with a transition in everyother half-cycle.

FIG. 1J is another symmetrical waveform with a transition in every otherhalf-cycle.

FIG. 2A is schematic of a controlled transition power stage reproducedfrom the prior related applications.

FIG. 2B is a block diagram illustrating an improved triggering circuitand typical details of a distributable dimmer system.

FIG. 2C is a block diagram of one embodiment of a control signaldistribution system. FIG. 3A is a front elevation of a mechanicalembodiment adapted for mounting within the yoke of a fixture.

FIG. 3B is a side elevation of the embodiment of FIG. 3A.

FIG. 4A is a side elevation of an embodiment adapted for use as alamp-supporting clamp.

FIG. 4B is a rear elevation of the embodiment of FIG. 4A. FIG. 5A is aside elevation of a typical prior art power connector.

FIG. 5B is a front elevation of the power connector of FIG. 5A.

FIG. 5C is a front elevation of a prior art power receptacle.

FIG. 5D is a side elevation of the power receptacle of FIG. 5C.

FIG. 5E is a side elevation of a combined power and signal connector.FIG. 5F is a front elevation of the combined power and signal connectorof FIG. 5E.

FIG. 5G is a front elevation of a combined power and signal receptacle.

FIG. 5H is a side elevation of the combined power and signal receptacleof FIG. 5G.

FIG. 5I is a side elevation of a signal connector.

FIG. 5J is a front view of an improved power and signal receptacle.

FIG. 5K is a front view of an improved power and signal connector.

FIG. 5L is a side elevation of the connector of FIG. 5K.

FIG. 6A is a side elevation of a mechanical embodiment adapted forraceway use.

FIG. 6B is a reverse plan view of the dimmer of FIG. 6A.

FIG. 6C is a sectional view of FIG. 6A.

FIG. 6D is a side elevation of a second variation of a dimmer adaptedfor raceway use.

FIG. 6D(a) is a section through a possible embodiment of dimmerenclosure 609B of FIG. 6D.

FIG. 6D(b) is a side elevation of the dimmer enclosure 609B of FIG.6D(a).

FIG. 6E is a sectional view of FIG. 6F.

FIG. 6F is a side elevation of a third variation of a dimmer adapted forraceway use.

FIG. 6G is reverse elevation of the interior of one side casting of theembodiment of FIG. 6D.

FIG. 6H is a reverse plan view of FIG. 6F.

FIG. 6I is a section through FIG. 6G.

FIG. 6J is a plan view of the casting of FIG. 6F.

FIG. 6K is a section through the casting of FIG. 6F showing thecompartment for electronics.

FIG. 6L is a section through the casting of FIG. 6F showing the surfacefor mounting semiconductor power devices.

FIG. 7A is a front elevation of a fourth mechanical embodiment.

FIG. 7B is a front elevation of the backbox of the dimmer of FIG. 7A.

FIG. 8A is a plan view of a mechanical embodiment adapted for portabletheatrical use.

FIG. 8B is a front elevation of the embodiment of FIG. 8A.

FIG. 8C is a plan view illustrating one application of the embodiment ofFIG. 8A.

FIG. 8D is a front elevation of FIG. 8C.

FIG. 8E is a section through a second variation of a dimmer enclosureadapted for portable theatrical use.

FIG. 8F is a section through a third variation of a dimmer enclosureadapted for portable theatrical use.

FIG. 8F(a) is a diagram illustrating an alternate design for the area ofenclosure 809E of FIG. 8F to which semiconductor power device 519F isattached.

DETAILED DESCRIPTION

Referring again to FIG. 1A, the drive or triggering circuit 404 may beanalog open loop; or, with the appropriate sense input analog fed-back(as disclosed in U.S. Pat. No. 3,397,344); or digital (as disclosed inU.S. Pat. No. 4,241,295).

The means to control the transition, illustrated as transition controlmeans 406, may comprise a separate hardware circuit, whether analog,digital, or a software function; or it may be partially or fullyintegrated into the triggering circuitry or the device drivers.

Similarly, the output devices, illustrated as power controller means419, may be of any known type suitable for the purpose.

Such devices must satisfy certain basic requirements. Foremost is theability to withstand the high instantaneous power dissipation which ischaracteristic of the power stage's operation, for while the thermalload is relatively modest if averaged across the half-cycle, it isconcentrated in the transition period.

Given both suitable instantaneous and average power ratings, devices arethen selected on the basis of drive characteristics, protectioncharacteristics, and conduction losses.

Over the longer term, the use of devices fabricated on silicon carbideor diamond film will be attractive, in that they permit far higheroperating temperatures, permitting the use of substantially smaller heatsinks.

Refer now to FIG. 1B, a block diagram of the improved dimmer of thepresent invention adapted for the use of devices having an inputvoltage/output current relationship, such as field effect devices. Partswith the same function in FIG. 1A are identified with the same referencenumber.

The input voltage at the gate of a field effect device controls itsoutput current. Therefore, for a given input voltage in the device'slinear region, the actual voltage at load 499 is a factor of theimpedance it presents, which varies with the number of filamentsconnected and their temperature. This mechanism has no effect on thedimmer when off or in full conduction, but during the transition periodit results in variations in the duration of the transition withvariations in the load impedance - and as such, undesirable variationsin average power, audible lamp noise, and thermal losses in the devices.

Although dimmers with overall feedback in the triggering circuit (suchas disclosed in U.S. Pat. No. 3,397,344) compensate for the effect onaverage power, they do not correct for the variation in the duration ofthe transition, and with it, variations in audible noise and thermallosses.

Preferably a controlled transition power stage corrects this variationby controlling the rate at which voltage rises (or falls) during thetransition. This object may be achieved by the use of a semiconductorpower controlling means with an input voltage/output voltagerelationship (such as a power transistor in an emitter-followerrelationship). Where devices having an input voltage/output currentrelationship are employed, means for this correction is required,illustrated in FIG. 1B as a transition feedback circuit comprisingdifferential amplifier 421 interposed between transition control means406 and the gate input 420 of the power devices 419, accepting as itssecond input, the dimmer output voltage via conductor 412 and feedbacknetwork 414. Feedback network 414 shapes, rectifies, or attenuates theload voltage derived from load 499, as may be required. Some embodimentswill provide two means analagous to amplifier 421 and network 414, oneprovided for each half-cycle. The actual output voltage produced by theinteraction of the current resulting from a given gate input voltagewith the impedance of load 499 is compared with the desired value, andthe gate input voltage corrected accordingly. Such a power stage istherefore capable of maintaining the same duration of transition at eachphase angle and as such, consistent curve, audible noise, thermal lossesand EMI suppression despite variations in load impedance.

The gate voltage/output current relationship of field effect devicesalso permits limiting output current by limiting maximum gate inputvoltage. Accordingly, FIG. 1B illustrates zener diode 423 as clampingmaximum gate voltage.

The parent applications No. 943,381 and grandparent application No.640,978, now U.S. Pat. No. 4,633,161, included in their entirety byreference, disclose suitable circuits in detail.

LONG TIME CURRENT LIMIT

The dissipation limiting circuit and gate clamp illustrated in FIG. 2Aof the grandparent application, now U.S. Pat. No. 4,633,161, serves toprotect the power devices from fault conditions caused by abnormally lowimpedance, but steady state overloads such as may be produced byplugging a 2000 watt lamp into a 1000 watt rated dimmer may not causethem to trip. While a circuit breaker or conventional fuse may beemployed, they serve to increase the size, complexity, and cost of thedimmer. Nor are they remotely or automatically resettable. Accordingly,it is desirable to employ a long-term current limiting method for sucheventualities. Because the dissipation of a controlled transition dimmeris greatest near a 90 degree conduction angle, limiting the RMS oraverage current will not necessarily limit dissipation to a safe value.Therefore, this "long-term current limit" should provide due weight tothe peak current, or to a current measurement taken in the second halfof each half-cycle (or the first half, in the case of a "turn-off"dimmer).

IMPROVED TRIGGERING CIRCUITS

Refer now to FIG. 2B, where an improved triggering circuit particularlysuited to distributed dimming applications is illustrated.

All phase control dimmers require a triggering circuit that functions asa timer whose delay between zero-crossing and triggering the change instate of the power device is determined by the desired average powersetting (as represented by a corresponding value present at its controlinput).

Most prior art dimmers have employed analog circuitry for this function,but the performance of such circuits is frequently dependent upon notjust circuit design but component variations and temperature.

Many dimmers (such as that disclosed in U.S. Pat. No. 3,397,344) haveemployed negative feedback to reduce such variations, but classicalfedback triggering circuits have an inherent "curve" or family ofcontrol input value/output power relationships that is less than ideal.There has therefore been a tendency to modify such circuits to produce amore desirable curve, at the cost of stability.

Prior art analog triggering circuits, whether open-loop or fedback, haveproven difficult to design well and require regular adjustment ifconsistent response is to be maintained, both from month-to-month andfrom dimmer-to-dimmer. Such consistency has become more important withthe transition to dimmer-per-circuit, because the lamps on a commoncontrol channel are on separate dimmers, which emphasizes anydiscrepancies between them in response.

The "digital" dimmer, as generally disclosed in U.S. Pat. No. 4,241,295,is theoretically simple to design, immune to component variations, andcapable of reproducing any "curve" with total consistency. Severaldrawbacks have, however, become apparent. One is the difficulty ofproviding a line regulation scheme which compensates for real-worlddistortions in the AC waveform, and hence total power. Overall negativefeedback compensates for such variations, but while relatively simple toprovide analog circuits, such feedback (or an equivalent feedforwardfunction) is far more complex to implement in digital ones.

Digital triggering circuits also have higher parts costs than analogschemes, and therefore have generally been restricted to applicationswhere a single triggering circuit can be shared by as many astwenty-four power stages.

A distributed dimmer system places a premium on triggering circuitswhich are simple in design, cost-efficient in single dimmerapplications, are fully line-regulated, require little or no adjustment,and are highly consistent in response. FIG. 2B illustrates a "precisionanalog" triggering circuit meeting these objectives.

FIG. 2B illustrates a dimmer enclosure 199, containing one or more powerstages comprising a power controller 419 with an associated transitioncontrol means 406.

The transition control means 406 accepts a phase control input via 403from triggering means 404, which is illustrated as accepting an inputvia 404I, corresponding to a desired average power to be supplied tolamp load 499, and as responsive to the zero-crossing of the alternatingcurrent waveform detected via 404E.

Improved triggering means 404 is illustrated as comprising a phase angleconverter 404A which determines the relationship between the desiredaverage power condition at input 404I and the firing angle supplied tothe power stage. In a known manner, negative feedback (here illustratedas a differential amplifier 404B) is used to minimize the effects ofvariations in both input power and dimmer performance by comparing thedesired value with actual dimmer output as sensed via 412, and byadvancing or retarding the phase angle as required.

Unlike prior art dimmers, the dimmer of the present invention maintainsa closed loop gain of greater than 10 over its entire range ofadjustment. This has the effect of greatly increasing the stability ofdimmer performance over prior art, although it produces a less desirable"curve". This is corrected by deliberately distorting the control signalto the dimmer input 404I, such that the characteristic response of thefeedback network restores the input value/output voltage relationshipsto the desired "curve". Many methods of performing this correction arepossible. Here a curve correction means 404F, comprising an EPROM lookuptable, is inserted in the input at the digital level, although suchcorrection can be performed, less desirably, at the analog level.

In contrast to prior art designs, which limit closed loop gain andmodify feedback network operation to maintain an acceptable "curve" atthe cost of stability, the improved triggering means of the presentinvention uses unusually high closed loop gain to produce stability, andachieves the previously contradictory object of an acceptable curve bycompensation outside the feedback network.

Further, prior art triggering stages have employed a network 414B whichproduces a DC voltage approximately related to (and thereforestabilizing) average voltage at the lamp. Lamp brightness is, however,determined by RMS voltage. The relationship between average and RMSvoltage varies with changes in waveform shape produced by changes infiring angle, and therefore such dimmers cannot maintain stable lampbrightness with changes in line voltage. The use of a network whoseoutput is related to RMS voltage provides the basis for more accurateregulation, but the characteristic output of such circuits would producean unacceptable "curve". The use of such an RMS network 414B incombination with the disclosed precompensation technique permits thesignificant improvement in dimmer regulation produced by RMS voltagesensing, while maintaining an acceptable curve.

FIG. 2B further illustrates a typical application of such a dimmer in adistributable embodiment.

AC mains supply 171 is illustrated as supplying at least onemultiple-phase branch circuit distribution panelboard 173, includingcircuit breakers 175 providing overcurrent protection for a plurality ofbranch circuits.

Distribution panelboard 173, which may be permanently installed in afacility or designed for portable use, provides for the connection ofbranch circuits, whether by permanently-installed raceways and conduitsor by means of portable cables (such as 180) and connectors (such aspanelboard receptacle 176, and cable connectors 177 and 178). Suchcables and connectors may be single circuit or, as illustrated, multiplecircuit. Branch circuits are provided for a plurality of dimmerenclosures 199 at spaced apart locations, each in proximity to at leastone controlled fixture. The design of such enclosures may allow forplugs or inlets for power (such as 179, 621 of FIG. 6A, and 753 of FIG.8C); outlets for lamp loads (such as 181, 211 of FIG. 6B, and 211A-C ofFIG. 8B); and feed-thru outlets (such as 180, and 752 of FIG. 8A) topermit parallelling additional dimmers/enclosures to the same branchcircuits.

It will be understood that many applications will involve multiplelevels of branch circuit distribution. It will also be understood that adistributed dimmer enclosure may incorporate some level of branchcircuit distribution itself, for example, from a 20 or 30 Ampere supplyconductor to two or three 1000-watt rated dimmers.

Local potentiometers can be mounted on or located near the dimmerenclosure, but typically the system provides at least one known lightingcontrol console 150 to specify the desired average power to be suppliedto each of a plurality of controlled fixtures, and hence theirintensity, together with a means to couple the output condition of theconsole 150 representing the desired average power for a dimmer with theinput 404I of its triggering circuit 404.

This means to couple may take one of several forms, each well known inthe art.

A discrete parallel output 151P of lighting console 150, typically ananalog voltage varying between 0 and 10vDC, may be supplied to eachdimmer or group of dimmers responsive to that given output.

A serial output 151S of lighting console 150, either analog or digital(e.g. conforming to the serial standards of the United States Instituteof Theater Technology, New York, N.Y.), may be supplied to all dimmers,each dimmer or group of dimmers employing a multiplex decoder 160 whichis set for its own address to recognize the appropriate desired averagepower value in the serial data stream.

Separate cables and connectors may be employed for power and signal orcommon connectors and/or cables employed.

Alternatively, a serial output of lighting console 150 may be suppliedto known power line communications transmitter 155, which impresses acoded data stream on the AC supply 171 via outputs 156X-Z. Knowndetector circuitry 157 at the dimmer strips the data from the powerlinefor demultiplexing. The widely-employed "BSR" system sends commandswhich increment or decrement the desired average power values held in aregister at the addressed dimmer. The actual desired average power valuemay also be transmitted.

Preferably, a common integrated circuit or package, together with switch160S and diodes at the input 404I to triggering circuit 404 permit thedimmer to accept parallel, serial, or powerline signal inputs.

Inexpensive power line communications hardware places severe limits onmaximum baud rate. Due to this limited baud rate, neither system issuitable for most professional applications because the time requiredfor each dimmer adjustment makes it impractical to execute "cues" inwhich large numbers of dimmers transit from old to new values inapparent simultaneity.

If, however, a short-term memory means is provided at the dimmer, suchthat a plurality of desired average power values can be stored, eachreferenced to an identifying "preset" or "cue" number, then the outputof that number by the lighting console 150 over the power linecommunications transmitter 155 could cause an unlimited number ofdimmers to transit to new values simultaneously, well within the limitedbaud rate of the system.

Refer now to FIG. 1C, a more detailed block diagram of a dimmerincorporating various of these improvements.

At the core is a simple, known open-loop phase control triggeringcircuit 404A that accepts an analog voltage at its input and produces achange in the state of its output at the desired firing angle.

This triggering circuit is part of a feedback loop formed bydifferential amplifier 404B that compares the input value with thedimmer's output voltage.

This feedback loop has a high gain--in excess of 10:1, the advantages ofwhich have previously been described.

A RMS-to-DC converter 414B may be placed between the input to thedifferential amplifier 404B and the dimmer's AC output so that thefeedback loop stabilizes RMS voltage, the advantages of which have alsopreviously been described.

A byproduct of the simple triggering circuit 404A, the unusually highnetwork gain, and the sensing of RMS voltage is an undesirable "curve".

As previously described, this can be corrected without the priorundesirable compromise of the efficacy of the feedback loop byperforming a curve correction external to that feedback loop.

In the embodiment of FIG. 2A, the digitally-expressed desired intensityvalue produced by the control console may serve as an index to a lookuptable that contains a second value corrected for the effects of thefeedback network. This corrected value is supplied to the dimmer.

It will be apparent that such a correction table, (which requires only256 1-byte values) can be used not just to correct curves but, as thereis no limit on the degree of correction, to change them.

The result is a dimmer triggering stage having a very low level ofelectronic complexity, and thus which can be provided on a one powerstage/one triggering stage basis.

The dimmer's unusually high level of feedback can produce stability thathad previously been limited to more complex processor-based "digital"dimmers, while offering the "curve on a chip" feature traditionallylimited to such digital dimmers as well.

However, the disclosed dimmer has an ability to compensate for "realworld" variations in the AC supply that recent dimmers that share asingle triggering stage among multiple power stages--and particularly"digital" dimmers--have found it difficult or impossible to provide.

"Feedback" as to the actual state of the power output of a dimmer hastraditionally been expensive to provide, even in analog dimmers, becauseof the requirement for voltage isolation between line voltage and thelow voltage at which the triggering stage operates. This requires theuse of a step-down transformer between the input to the triggeringcircuit and the line voltage output of the dimmer, which addssignificantly to both the size and the cost of the dimmer triggeringstage.

It was the size and cost of this feedback transformer which, gratingagainst the "value engineering" requirements of high-density dimming,was one factor in the abandonment of fully fedback operation by manyrecent dimmers--an action that proved to have been premature.

An interim solution to the problem of voltage isolation has been the useof capacitors to provide some measure of such isolation, but has notproved an entirely satisfactory one.

Another difficulty with triggering circuit design has been therequirement for low-voltage power supply to it. As the triggeringcircuit must be isolated from the AC line and operate at low voltages, aDC power supply is required for its active electronics. This, in turn,required another step-down transformer in traditional dimmer design, onethat further increased the size and cost of triggering stageelectronics. In some systems, DC power supplies were shared amongmultiple triggering circuits, and the reduction in the number of powersupply transformers was a not-inconsiderable benefit of centralizedtriggering circuit designs.

FIG. 1C illustrates how a fully-fedback individual triggering stage canbe provided for each power stage without the previous requirement foreither a feedback transformer or a power supply transformer.

Prior art triggering stages placed the voltage isolation barrier betweenthe control system and the AC power line at the interface between thetriggering stage and the power devices; first with pulse transformersand subsequently with optoisolators.

By moving the low-voltage/high-voltage barrier to the input instead ofthe output side of the triggering circuit, the triggering circuit'selectronics can be allowed to float at or near line level. This permitsthe feedback system to be coupled to the AC output of the dimmer and theactive electronics to be supplied without the requirement for atransformer for either function, at a very significant decrease in thesize, weight, and cost of the triggering circuit.

There are several methods of performing that isolation at the input sideof the dimmer's triggering stage.

One of the simplest is opto-isolation, which can be readily employed asmost professional dimmers can accept a digital input.

FIG. 1C illustrates a dimmer whose input value, sent by an LED, isreceived by photodetector 160I. That value is held by register 162R, andconverted to the analog input voltage to the triggering stage by D/Aconverter 162D.

FIG. 1C also illustrates that processor 400A can be used in the overalldesign of the dimmer. While such a processor can be employed, it hasbeen seen that it is not necessary for any of the functions previouslydescribed. However, if provided, it can serve several functions, one ofwhich would be the servicing of a serial input, and another the curvecorrection function.

In the latter case, the processor's Curve Correct Store 400X holds thevalue corrected to produce the desired "curve".

Although many of the previously-described techniques can be used withinductively-filtered power stages, the power stage illustrated in FIG.1C is of the "controlled transition" type.

The output of the triggering stage is provided to a transition controlsection. This includes a ramp generator 406A that is responsible forproducing a transition with the desired profile. That profile or thevalues required to calculate it are stored in Ramp Profile Store 400Yand provided by the processor to a buffer store 406R. Upon the statechange at the output of the triggering stage, ramp generator 406Aproduces a transition of the semiconductor power devices 419 betweentheir non-conductive and conductive states having the specified profile.Current sensor 451C and comparator 421 form a second feedback loop thatis responsible for compensating for variations in device performance andload impedance. Current information will also be used forcurrent-limiting.

Because the processor is provided with the desired intensity value andspecifies the transition ramp profile, the duration of that transitioncan readily be varied across the range of possible phase angles tomaximize EMI suppression.

By predetermining the maximum duration allowable within the dissipation"budget" at each phase angle, and by programming, for example, aduration multiplier value indexed to each such phase angle, theprocessor or ramp generator can "stretch" the specified transition rampprofile over the maximum allowable duration.

Clearly, these functions can be provided entirely in hardware without aprocessor as well.

It is also possible to vary the shape of the transition ramp profileover the range of phase angles, either by means of a correction factorand/or by storing additional profiles in Ramp Profile Store 400Y, eachindexed to a subset of the range of possible input values.

Clearly, the dimmer can also store different profiles or profile setsfor different lamp types. The dimmer can be "told" which type of lamp isattached by a switch selection. Or it can be told over its digital inputfrom the console, for example, by a lighting database program.

But different filaments, by virtue of their different thermal masses anddesigns, have different responses to current, and so, by providing thecurrent sense information developed by sensor 451C to processor 400A viaA/D converter 453A and register 453R, processor can "stimulate" theconnected load and observe its response via current sensor 451C. Bycomparing its observations with stored data for different lamp types,the processor can determine which lamp type is connected and so choosethe appropriate transition ramp profile automatically.

With the presense of a microprocessor and the current sensing feature aswell as other status information, the dimmer can make manydeterminations about the status of both itself and the connected loaduseful for the controller and user to know. For this purpose, aninexpensive power line carrier chip 157 is provided for low-speed statusqueries and reports over the AC supply wiring. Other means may beemployed.

Preheat is employed to reduce the range of variations in the impedanceof the connected filament(s), and with it, in the current demands on thesemiconductors. This preheat function can be provided with a time-out toconserve power and/or turned off when serial transmissions to the dimmercease.

USE OF ASYMMETRIC WAVEFORMS

Controlled transition dimmers impose significant dissipationrequirements on the semiconductor power devices they employ. The use ofunconventional waveforms to reduce thermal losses was first suggested inthe grandparent application, now U.S. Pat. No. 4,633,161. In some cases,the use of asymmetrical waveforms may permit a reduction in devicedissipation.

AC dimmers and other power control apparatus with asymmetric waveformsfrom half-cycle to half-cycle are known. The simplest such dimmer is theskipped half-cycle design, which has the advantage of switching only atthe zero-crossing. Unfortunately, it also has the disadvantage ofinsufficient resolution for professional use, given the relatively lowfrequency of the AC supply. It is, for example, easy to achievehalf-power by skipping alternate half-cycles, but hard to produce 52%power.

The strategy of dropping entire half-cycles may, however, be combinedwith one of attenuating selected half-cycles as well.

Refer now to FIG. 1E, that of a conventional "turn-on" phase controldimmer at slightly more than half-power, and to FIG. 1F, the output of adimmer producing slightly more than half-power by permitting the passageof one entire half-cycle and a small portion of a second one. Theresult, when averaged out by the thermal mass of the lamp filament, isequivalent to the more conventional output of FIG. 1E, but involves onlyhalf the number of transitions, and they are at a lower voltage acrossthe device.

Achieving such operation is relatively simple, processor 400A, forexample, can consult a lookup table. The result of the asymmetry of thewaveform is a high DC component in the output and the possibility offlickering of lamps with low thermal mass.

Another approach to minimizing voltage across the devices duringtransitions is to alternate two different phase angles that average outto the desired value.

The same average voltage produced by the conventional waveform of FIG.1E could also be produced by alternating between firing very early andvery late in the half-cycle, as is shown in FIG. 1G. While there is onetransition in each half-cycle, it takes place closer to thezero-crossing than that of either FIGS. 1E or 1F.

The two techniques can be combined, as shown in FIG. 1H.

This combined technique would produce the desired average voltage byfirst, skipping half cycles; second, "fine-tuning" these grossadjustments by incorporating partial half-cycles; and, third, furtherminimizing the voltage potential across the devices during a transitionby substituting pairs of two partial half-cycles with greater and lesserphase angles averaging out to the desired average power.

It would also be possible to use the power device in a linear mode forselected half-cycles.

However, each of the waveforms of FIGS. 1F-1H, by virtue of itsasymmetry, possesses a high DC content, which prevents its use withballasted lamps (such as flourescents) and with fixtures incorporatingstep-down transformers (i.e. those employing low-voltage bulbs). Theasymmetrical current demands of a number of such dimmers may alsodecrease the efficiency and may overheat a stepdown transformersupplying such dimmers. The effects of the DC component on lamp life,contact arcing, and filament noise are also not clear.

Refer now to FIG. 1I, where a dimmer waveform is illustrated having theadvantage of the reduced dissipation of FIG. 1F, but providing asymmetrical output. It will be seen that, for example, by inverting thepolarity of the output waveform of FIG. 1F with each successive fullcycle, that a symmetrical waveform is reestablished, i.e. thathalf-cycle "a" of FIG. 1I balances half-cycle "d" and that half-cycle"b" balances half-cycle "c".

FIG. 1J illustrates that, with the use of a reverse phase-control "turnoff" output, the waveform can be made symmetrical across azero-crossing, such as that between half-cycles "b" and "c" That is,from a setting of "off", transitions will advance symmetrically from the"b/c" zero-crossing through the "b" and "c" half-cycles. Upon reachinghalf power, half-cycles "b" and "c" will be on and half-cycles "d" and"e" will be off. Increases above half power will advance the "turn-on"transition through half-cycle "a" and the "turn-off" transition throughhalf-cycle "d" until all four half-cycles are on.

The same technique of adjacent "turn-on" and "turn-off" half-cycles canbe used for dimmers varying their output by means of a transition inevery half-cycle.

As noted in the grandparent application, now U.S Pat. No. 4,633,161, insome cases, the most efficient reduction in thermal losses may beproduced by a dimmer that changes between several different outputwaveforms, depending upon the desired intensity value.

Such a dimmer can be produced by a simple extension of the CurveCorrection function by simply providing a catalog of patterns, indexedto form a range from full conduction to none, and incrementing alongthat index with a feedback function until the desired voltage for anygiven control value is achieved Other, hardware, designs producing thevarious waveforms illustrated will also be readily apparent.

CONSTANT DISSIPATION TRANSITIONS

Prior embodiments have illustrated power stages that stabilize rise (orfall) time despite changes in the connected load. A controlledtransition dimmer can also be built that increases rise time with lowerwattages and at phase angles where its dissipation "budget" permits Infact, as the limiting factor on rise time is device dissipation, one cansense or predict device dissipation and use a feedback function tomaximize rise time within that dissipation "budget". Doing so by sensingdevice temperature has the added benefit of integrating the effects ofthe local ambient temperature.

PREHEAT

The decreased impedance presented by a cold lamp filament has long beenknown to produce current inrushes which may strain the semiconductorpower controlling means. Such semiconductors must be oversized relativeto their normal operating currents (or conversely, derated) and/or acurrent-limiting method be provided that limits the current let-throughin each half-cycle so that the filament is warmed over a number ofhalf-cycles to the point at which its impedance has risen (and currentrequirements fallen) to acceptable levels.

Both methods have disadvantages "Over-speccing" or "under-rating" arecost inefficient. The use of current-limiting (or a ramp at the drivestage as disclosed in U.S. Pat. No. 3,898,516) to gradually warm thefilament produces a delay in response which may be unacceptable in someapplications.

A means may be provided, however, for preheating the lamp for thepurpose of increasing the power-handling ability of a givensemiconductor by decreasing the difference between off-state andon-state load resistance.

Such preheat circuits have proven to reduce the on/off state resistanceratio from 10:1 to 4:1.

PHYSICAL EMBODIMENT OF FIGS. 3A AND 3B

Refer now to FIGS. 3A and 3B where a first mechanical package for thedisclosed dimmer is illustrated.

The use of a distributed dimmer that is functionally integral with thefixture it controls has long been a desirable object, in part because itpresents no incremental increase in handling labor. Ideally, the dimmerwould be contained within the fixture yoke, but the volume of a dimmerfiltered to professional standards would exceed the clearances availablebetween most production fixtures and their yokes. This would require thesubstitution of a custom, elongated yoke which is less than desirablefor a variety of reasons. More commonly, dimmers of this type have beenattached to the exterior of the fixture yoke. In this location, theysignificantly reduce the maximum number of fixtures which can beemployed on many types of lighting position, by increasing the minimummounting centers. They may reduce the number of fixtures that can beaccomodated in some types of shipping crate; may hinder access to thefixture during focusing; and are vulnerable to damage during handling.

Referring to FIGS. 3A and 3B, fixture 301, illustrated as anellipsoidial reflector spotlight (such as manufactured by Colortran,Inc., Burbank, Calif.), includes a formed metal yoke 303 which allowsvertical adjustment about an axis through handwheel 305 and bolt 306.Yoke 303 is, in turn, attached via bolt 311 to the fixture mountingposition, here illustrated as via the stud 310 of a standard "C-clamp".Freed of the requirement for a bulky filter inductor the discloseddimmer may be accomodated within a housing 309, here illustrated as analuminum casting, designed to conform to the interior surface of yoke303. Heat sink fins 317 are cast into enclosure 309, with an interiorprofile that provides adequate clearance for fixture 301 in allorientations High-temperature lead 321 connects the fixture with thedimmer, lead 319 connects the dimmer with power and signal inputs.Additional controls including an address thumbwheel switch 315, signalindicator, neon pilot light, and self-test button are provided. Housing309 provides a pass-hole for bolt 311, which is inserted through bothhousing 309 and yoke 303 into the internally-threaded portion of stud310, mounting fixture and dimmer in the same operation. Alternatively, aU-shaped slot may be provided with a well to accept the bolt head orwasher, such that the dimmer can be removed without requiring that thebolt 311 be completely removed. Alternatively, the dimmer enclosure mayclip onto the yoke.

The embodiment of FIGS. 3A and 3B thus achieves the long-desired objectof mounting a dimmer to its fixture with none of the disadvantages ofprior art units. For the first time, professional standards ofperformance are achieved with no increase in fixture bulk, minimummounting centers, or shipping volume.

PHYSICAL EMBODIMENT OF FIG. 4A AND 4B

FIGS. 4A and 4B illustrate a second mechanical embodiment.

As an alternative to mounting a dimmer on the fixture itself, some priorart distributed dimmer schemes have employed single-dimmer enclosureswhich attach to the same mounting position as the fixture rather than tothe fixture itself. The resulting boxy enclosures compete with thefixtures for location on the pipe or rail and complicate the mountingand movement of fixtures as well as access to them.

FIGS. 4A and 4B illustrate that the disclosed dimmer permits anembodiment uniquely capable of conforming to the mounting position. Thedimmer enclosure can be designed as a substantially cylindrically-shapedcollar that surrounds the pipe from which fixtures are most commonlyhung. Here, the function of the dimmer enclosure has been furthercombined with that of the clamp that attaches the fixture to themounting position.

Referring to the Figures, the disclosed dimmer has been installed in ahousing 109, here illustrated as fabricated from an aluminum extrusion,which includes the basic profile of a "C-clamp" which grips steel pipe127 by tightening bolt 129 in the prior art manner. Stud 310 is providedfor the attachment of the yoke 303 of any lighting fixture, using bolt311 as previously described. The external surface of housing 109 isprovided with heat sink fins 117, and some additional sinking may resultfrom conduction through pipe 127. High-temperature lead 321 connects thefixture with the dimmer; lead 319 connects the dimmer with power andsignal inputs. Additional controls including an address thumbwheelswitch 315, signal indicator, neon pilot light, and self-test button areillustrated.

The disclosed dimmer in the embodiment of FIGS. 4A and 4B thus achievesthe desirable object of attaching the dimmer to the same mountingposition as the fixture with none of the disadvantages of previousmethods. Fixture and dimmer are mounted and moved in a common operation,with no undesirable increase in bulk at the position.

IMPROVED POWER AND SIGNAL CONNECTOR

The use of distributed dimmers as illustrated in the previous Figuresrequires providing both power and signal, whether multiplexed ordiscrete, by means of portable cables and temporary connections. Whileseparate cables and connectors can be used for each function, in manycases it would be desirable to employ a single connector for both. Whilemulti-pole multi-connectors have been employed to distribute both powerand signal in other performance lighting applications, such connectorsare difficult to field install and have no commonality with industrystandard power connectors.

Refer now to FIGS. 5A-5I, where an improved connector system forsimultaneously distributing power and signal is illustrated.

FIGS. 5A and 5B illustrate a 20A 125VAC grounded "pin" connector 201(such as the model 2P&GMC as manufactured by Union Connector Co., Inc.,Roosevelt, N.Y. 11575) which has long been the standard of the industry.The connector 201 provides split brass pins 203 for hot, neutral, andground. Flexible conductors such as cable 209 enter the connector bodyvia a molded-in strain relief, and the individual conductors areterminated using uninsulated ring crimps.

FIGS. 5C and 5D illustrate a mating panel-mounted receptacle 211 (suchas the Model 2P&GF-FL by the same manufacturer). Similar cable-mountedreceptacles (such as the model 2P&GFC) are also available.

FIGS. 5E and 5F illustrate an improved connector 221 for both power andsignal. The power portion of the connector body duplicates the body ofconnector 201. However, a well 225 is added to accommodate an insert 227mounting pins 223 for the low-voltage signal connection. Such pins couldbe installed captive to the body of connector 221, but preferably aremovable insert 225 is employed, and accordingly a retaining barrier226 is illustrated. The use of a removable insert has the benefit ofallowing the use of a stock low voltage connector insert (such asmanufactured by Hypertronics Corp., Hudson, Mass. 01749), reducing thecost of developing connector 221 to little more than enlarging the diefor the body of connector 201. Further, different termination techniquesmay be employed for the power and the signal conductors, and thetermination operation for the latter performed outside the connectorbody. While a rectangular insert with three parallel pins isillustrated, it will be understood that it may be desirable to employ acircular "XLR"-type insert (such as manufactured by ITT Cannon Electric,Santa Ana, Calif. 92702).

The body of connector 221 is provided with dual strain reliefs to allowthe use of separate power and signal cables 228 and 229 or a commoncable for both functions.

FIGS. 5G and 5H illustrate a mating panel-mounted receptacle 231 (and,by extension, a cable-mounted receptacle). A protruding enclosure 235for the signal insert 237 is cast into the receptacle body. It will beapparent that one benefit of this arrangement is that the smaller malesignal pins 223 can be shrouded by the body of connector 221 forprotection from damage in handling. It will also be apparent that anyimproved connector 221 can be mated with a conventional receptacle 211,and that any conventional connector 201 can be mated with an improvedreceptacle 231. Thus, any cable constructed with the improved connectorremains completely "downward-compatable" with conventional dimmingequipment, vastly simplifying the user's inventory.

Alternatively, a combined signal and power connector body can beproduced by attaching (either temporarily or permanently) a housing 241for the signal insert 227 to a power connector body 201, hereillustrated as by means of dovetail joints 219 and 249 cast into thefinger grips. Similarly, the plug or receptacle may incorporate anadaptor to an RJ-11 or similar modular jack, allowing a transition toprefabricated signal cables.

Multi-phase versions of the connector can also be readily produced.

It will be apparent that the disclosed connectors with suitable cablingprovide a common, integrated means of supplying both power and controlnot only to distributed dimmers, but also to motorized and automatedfixtures and accessories, again, in a manner compatible with prior artcables and connectors.

PHYSICAL EMBODIMENTS OF FIGS. 6A-6M

A third mechanical embodiment is illustrated in FIGS. 6A, 6B, and 6C.

As previously described, a practical distributed dimming system wouldoffer important practical advantages in permanent installations Noelaborate system of carefully identified conductor pairs would berequired between the fixture positions and distant dimmer racks, norneed spaces be set aside for the latter which must be ventilated andsound-isolated. Instead, the use of a fully distributed dimming schemewould permit the installer to connect the receptacles on the connectorstrips with conventional circuit breaker panels, located in proximity tothe supplied circuits in a manner calculated to maximize bothconvenience and economy. In the case of outlet boxes, the requiredbranch circuit distribution breakers could be made integral with thedimmer enclosure, such that only power feeders and a signal conductorneed be supplied to the unit. Alternatively, particularly where accessto the fixture position is limited, the dimmer enclosures can be mountedat a nearby location, such as, for example, above the catwalk or in avertical array on the studio or auditorium wall. The thermal loadpresented by the dimmers in any of these embodiments would bedistributed throughout the performance area, hence no special cooling orventilating provisions would be required.

In the case of connector strips, a prior art fully distributed schemehas been proposed in the form of connector strip in whose elongatedmetal enclosure thyristor dimmers are installed. Such a scheme has manydisadvantages. The use of the connector strip as the mounting enclosuremay result in an undesirable internal heat rise caused by thethyristors, and particularly by the choke--one which is aggravated bythe lack of internal ventilation and the elevated ambient airtemperature produced by nearby fixtures. The bulk of the choke reducesthe crosssectional area of the enclosure available for wiring. Theinternal mounting of the dimmer components also makes service verydifficult given the dimmer location.

Refer now to FIGS. 6A-6C, where a third mechanical embodiment isillustrated.

Elongated raceway enclosure 641 mounts a plurality of receptacles,spaced as desired. Unlike conventional prior art connector strips,receptacles are provided for both power and signal. Separate receptaclesmay be provided for each function, but a common receptacle (hereillustrated as receptacle 231 of FIGS. 5G and 5H) may be employed.

While improved dimmer of the present invention could be installed in theraceway enclosure 641, it has been installed in a housing 609, hereillustrated as an aluminum casting, which is independent of racewayenclosure 641. Housing 609 has been provided with an inlet connector621, illustrated as a panel-mounted version of connector 221 (asillustrated in FIGS. 5E and 5F), which supplies power and signal fromreceptacle 231. An outlet receptacle 211 (as illustrated in FIGS. 5C and5D) is provided for the lamp. Address selector switch 315 and additionalindicators and a self-test switch are provided adjacent to connector211. Housing 609 has been illustrated with cast heat-sink fins 617.

Alternatively, the outlet receptacle 211 for the fixture may be mountedto the raceway enclosure 641, and the dimmer provided with an inletconnector 621 with two "hot" poles, one for supply and one to return thedimmer output to the raceway enclosure 641 for connection to lampreceptacle 211. It will further be understood that separate, parallelraceway enclosures may be provided for power and signal, oralternatively, that an internal partition may be installed in racewayenclosure 641 to separate the two conductor types. It will also beunderstood that continuous busses may be employed for power and/orsignal conductors, and that in some embodiments, the dimmer enclosuremay be provided with an inlet connector which attaches directly to thebusses. It will further be understood that control signals signal may bedistributed in parallel rather than serial form, and that in serialembodiments, the dimmer address may be predetermined by the receptacleitself.

Many designs for housing 609 are possible, and should not be understoodas limited except by the claims. It is here illustrated as having aprofile, visible in FIG. 6C, including a recessed portion having a shapecomplementary to that of raceway enclosure 641, such that when connector621 is mated with receptacle 231, the dimmer produces only a modestincrease in the bulk of raceway enclosure 641. This arrangement has theadded benefit of assisting in aligning connector 621 with receptacle 231during mating, and of protecting both connectors from damage caused byshear forces should the dimmer enclosure be struck an accidental blow.

As will be seen, such a system can be designed with the module plugginginto the top of the raceway, with the advantage that gravity keeps themodule in place and no locking means is required.

A module can plug into the raceway from the side as well, although thetop and bottom mounts offer two large vertical surfaces forheat-sinking.

One approach to retaining the bottom mount would include a magnetattached to the module that is attracted to the raceway or a plate orsecond magnet on it. Another approach is a latch or spring on the modulethat snaps into a groove extruded in the raceway or over its top edge.

In any of these embodiments, a locking mechanism may be provided thatprevents unauthorized removal of a module from the raceway, andelectronic an access code that must be transmitted at each power-up isalso possible.

The embodiment illustrated in FIGS. 6D and 6E uses a captive pigtailsuch as 205B attached directly to the raceway 641 in the prior artmanner. As previously described, a receptacle 232 is provided on theraceway into which a dimmer module can be plugged, placing it in seriesbetween the AC supply and the load connector 206A or 206B.

Such an approach has certain advantages, but requires some connectionacross the receptacle 232 to energize the pigtail 206A, for example, asa hot-patch.

Such a connection could be provided by a switch, but that has thedisadvantage of increasing the per pigtail cost of the raceway andintroducing a potential source of failure.

A shorting plug is a simpler alternative to a switch, but represents aloose component.

Refer now to FIG. 5J. Connector 232 is based upon the known Harj-Lokflush mounted receptacle as previously described--indeed it can beproduced by enlarging the die for that connector. That portion of therevised connector 232 to the left of line 232L is the same as thepresent Harj-Lok, including a hot contact 213H, ground contact 213G, andneutral contact 213N. The receptacle 232 is, however, enlarged toinclude provisions to the right of line 232L for a fourth "return"contact 213R.

When connector 232 is inserted in raceway 641, the hot, neutral, andground conductor from the AC supply are coupled to contacts 213H, 213G,and 213N. Contacts 213G and 213N are also parallelled with theappropriate conductors of the pigtail 205. The hot conductor of pigtail205 is connected with contact 213R of receptacle 232.

Dimmer module 609 includes four male pins 622 that supply hot, neutral,and ground to the dimmer and return its output to the load via thepigtail. By employing for connector 232 the same contacts and contactspacings for hot, neutral, and ground as the standard Harj-Lokreceptacle, however, the user can gain a "hot pocket" without the needfor a shorting plug by plugging a cable with a standard pin connectormale directly into receptacle 232. The spacing of contact 213R relativeto 213N assures that the male connector cannot be misplugged into thewrong set of contacts.

Receptacle 232 can be further enlarged to include a well 232S for asignal connector and/or LED as indicated by dashed outline 232D.

FIGS. 6D and 6E illustrate one possible physical embodiment of thedimmer module, which is shown as assembled from two identical casingssplit along the plane 609L. When assembled, the castings captivate theillustrated circuit card and connector in the lower chamber created bythem as well as the connector 622. The design of the castings providesheat sinks with pin fins 617P on both the inner and outer surfaces ofeach side panel. The pin fins on the interior surface of the sidepanels, combined with openings at the bottom, allow the vertical passageof air between the sides of raceway 641 and the side panel casting ofthe dimmer module, increasing the useable heat sink area. The fins orpins on the interior of the side panels also space the panel itself awayfrom the raceway, allowing clearance for the mounting of devices on theside panel itself (rather than below it as is illustrated).

Refer now to FIG. 6F-6M, where such a mechanical embodiment isillustrated in further detail.

Like the mechanical embodiment of FIG. 6D and 6E, the embodiment of FIG.6F-6M is designed as two symmetrical half sections joined along acentral plane. Unlike the embodiments of the previous Figures, theinstant embodiment, as shown in FIG. 6M, is designed to sit atop theraceway, with the advantage of requiring no mechanical means to retainit in place. It employs an inlet connector 622 plugging into areceptacle atop raceway 641F, and provides a pigtail 205C, which may beof any required length and may be terminated with any connector desired.

Referring to the various FIGS. 6F-6M, it will be seen that the enclosureconsists of two identical castings 609C and 609CC. The design of thiscasting, in the illustrated embodiment, may provide a chamber in theupper portion (as shown in FIG. 6K, a section) for the electronics,which may be mounted on a printed circuit card retained in slot 609T.Openings 609N are provided for LEDs indicating status, including thepresense of input power and signal, output power, and current-limiting,as well as pushbuttons for self-test and current-limit reset.

The male power inlet connector 622 may comprise male pins mounted to anelectrically-insulating plate retained in slot 622S. Male bosses 609Uand 609v of one casting interlock with spaces 609UU and 609VV of asecond to assemble a complete housing, which may be held closed by boltspassing through holes 609G and 609H.

The lower portion of casting 609C provides a large "ear" that hasseveral functions.

One function is to provide a mounting surface 609M for one or moresemiconductor power devices, along with a heat-spreading area and heatsink fins 609F for dissipation. The profile of this portion, illustratedin FIG. 6L, is of a gull-wing shape, providing clearance for thesemiconductor package or packages, which may be held in place by boltsthrough holes 609R.

A second function is to provide for power pigtail 205C, and for theconductors connecting it with the power devices and inlet connector 622.Accordingly, FIG. 6G-6I illustrate a U-shaped recess 609K that serves asthe "backrest" of a cable clamp, similar to that of the well-known"2-screw" or "Romex" connector. Holes 609S are allowed for passage ofbolts engaging the tapped holes in the floating portion of the cableclamp. Recess 609K is used for the power pigtail on only one of the twocastings that make up an enclosure, and the second such recess can beused for a Cannon "XLR" or Switchcraft "D" receptacle fastened tobulkhead 609H. The function of such a receptacle will be describedbelow.

The illustrated casting also provides standoff bosses 609QQ with boltsholes 609Q for a printed circuit card and/or insulator covering the areabounded by the lower bulkhead 909H and the electronics chamber.

Preferably, in volume applications of this and other mechanicalembodiments, a cast or extruded heat sink will be used in combinationwith FET die bonded to it (via an appropriate substrate, for example, asolder/moly drain pad and a BeO insulator) to obviate the need for aseparate package for each device. One method is to use a compositecircuit card such as the Thermal-Clad manufactured by Bergquist Co.,Minneapolis, Minn. 55435 as the die mounting surface, electricalinterconnect, and heat-spreader, with additional fins or pins bonded tothe back of the baseplate layer.

It will also be seen that it may desirable to isolate the activeelectronics from the heat produced by the power devices. Whileventilation of the electronics chamber is possible, another approach isto locate the electronics in a thermally-isolated section of the case.For example, a three-piece enclosure can be fabricated that consists ofaluminum or other thermally-conductive side panels (like thoseillustrated) mounting the power devices. The two may be separated by aspacer section fabricated of a thermally insulating or transparentmaterial (such as a thermoset, thermoplastic, or ceramic) or a metalsection simply mounted to the side panels by means of thermalinsulators. This spacer section may contain the electronics and maleinlet connector. The use of a material that is also an electricalinsulator permits mounting the pins of the male inlet connector directlyto the spacer section.

A related approach would employ an enclosure with side panels ofdifferent sizes; one, wide side panel would provide heat sinks for allpower devices, and the other, much more narrow, would house theelectronics. The two would be separated by a thermal barrier asdescribed, or the spacer/male inlet section and electronics sectioncould be fabricated as a single casting of thermally-insulating ortransparent material. Such an arrangement would have the benefit ofseparating the electronics from the heat produced by the power deviceswith the raceway, as well as placing virtually all the power wiring on asingle assembly.

The mechanical embodiment of disclosed dimmer illustrated in FIG. 6A-6Moffers a number of unique advantages. The unit can provide EMI andaudible lamp noise suppression meeting or exceeding the highest currentprofessional standards yet is totally silent under all loads and at allphase angles. The thermal design of the raceway enclosure 609 is alsosimplified.

Because the dimmer is mounted in an external, detachable enclosure,there is no significant reduction in the crosssectional area of theraceway enclosure 641, and hence in the space available for power andsignal conductors 643, nor are such conductors exposed to the increasein temperature produced by mounting dimmer components within the racewayenclosure 641 itself.

Further, service is simplified, as a failed dimmer is simply unpluggedand replaced with a spare. However, unlike dimmers employing bulkychokes, the profile of the dimmer can be minimized, and with it, theincrease in total connector strip/dimmer profile.

The illustrated embodiment has an additional important advantage.

The prior art distributed dimmer scheme described, whose dimmers aremounted permanently internal to the raceway, if installed in a facility,would offer the savings in installation costs previously described.However, it requires the installation of a dimmer for every outlet,which is hardly ideal in installations, like television studios, whichmay use only a fraction of their outlets at any one time.

The embodiment of FIG. 6A-6M offers a uniquely flexible alternative.Those installations which use a high proportion of their outlets canplug a dimmer enclosure into each one. Those installations with lowerutilization can maintain an inventory of dimmers slightly larger thantheir fixture inventory, and employ them on an as-needed basis. Indeed,both strategies can be used within a single installation, with a"dimmer-per-outlet" approach at some positions, and "dimmer-per-fixture"at others.

Further, as illustrated by connector 231 in FIG. 6A, the use ofstandardized power and signal connectors for the dimmer enclosure 609allows plugging "dimmer-on-lamp" units (as illustrated in FIG. 3A-4B)into the connector strip as well.

It will also be appreciated that the same outlets can be used to provideAC power directly to equipment like ballasted gas-discharge sources thatdo not need--or should not be connected to--dimmers, as well as bothpower and signal to motorized or automated fixtures or devices thatincorporate their own mechanical or electronic dimming means.

Finally, in the case of fixtures dimmed by any of the disclosedembodiments, a receptacle can be provided for control signals and/orline- or low-voltage power required by the accessory used by the dimmedfixture, most commonly a color changer. As previously noted, suchaccessories require a constant source of power as well as their owncontrol signals, which prior art centralized dimming and distributionsystems have not provided. The disclosed dimmer enclosures can beprovided with one or more receptacles providing means for supplyingeither line- or low-voltage power to the accessory and control signals,by means of a jumper between the receptacle and accessory. Such a jumper205D is illustrated in FIG. 6M, with its connector 206D plugged into areceptacle mounted at recess 609K of casting 609CC. By integrating thelow-voltage power supply in the dimmer enclosure, the size, weight, andcost of the accessory can be reduced. Further, the dimmer can decode notonly its own control signal from the serial data stream, but a separatecontrol signal for the accessory, at a minimal incremental increase incost. Ideally, the same serial address can be used for both the dimmerand its accessory with a different serial start code.

It will also be apparent that other types of dimmer power stage,including inductively-filtered thyristor-based designs, could be used,less desirably.

CONTROL SIGNAL DISTRIBUTION

Supplying desired intensity values to the dimmers requires a method ofreliably distributing the data to the various dimmer locations

There is also the issue of how the dimmers (or other users) determinetheir serial addresses. Because dimmers are readily removeable andinterchangeable, while address switches could be provided on them, thiswould require that the user match the address switch settings to theoutlet number every time a dimmer is installed or moved (if the userwishes the dimmer address to be the same as the outlet). As users cannotbe counted upon to do so, errors and the resulting confusion can beproduced.

In some applications (and in dimmer-on-lamp embodiments), a fixedaddress for each dimmer may be desirable, such that when the dimmer ismoved to another outlet it still retains the same address

In these and other applications, it may h=desirable to permit the userto remotely change the nominal address of a dimmer--or to add orsubstitute another value. Such other value could constitute the channelnumber, such that a "distributed signal patch" scheme results in whichthe data supplied to the dimmers represents the desired channel valuesrather than discrete dimmer values.

In those embodiments in which the dimmer is provided with its ownaddress, a means for indicating that address from a distance, such asLED displays or a large LCD or similar display.

In other applications, ideally, the address of the dimmer isautomatically set to that of the outlet when the dimmer is plugged intoit.

One method of doing so is to provide a means at each outlet uniquelyidentifying the outlet address, one which cooperates with a detectingmeans on the dimmer module. For example: an additional miniatureconnector wired with the binary-coded address; a bar code label sensedby photodetectors on the module; a binary-coded row of cams thatselectively actuate a DIP switch on the module.

All of these methods have some tradeoffs in cost, complexity, andreliability.

FIG. 2C illustrates a signal distribution scheme that addresses theseissues.

Each raceway section (e.g. section 641A and section 641B) mountsstandard pin connector (or other) receptacles 231A-231P. These are wireddirectly to supply circuit breaker panels.

Adjacent to or inset in each of receptacles 231A-231P is an LED, alignedwith a photodetector 160I in the dimmer module 609A. Desired intensityvalues and other data are coupled between the raceway and the dimmermodule by this means, which is simple, rugged, and reliable It providesthe voltage isolation required to float all of the dimmer electronics atline voltage, and protects all other dimmers and the console fromelectrical faults

The LED of each such receptacle is connected to a raceway "blob" module154A. Each raceway "blob" is connected to one output of a routing unit152 via a twisted pair cable carrying both RS-422 (or 20 mAcurrent-loop) data and power supply for the "blob" electronics. A singlesuch cable can be "daisy-chained" among multiple "blobs", or a discretecable run be provided between each "blob" and the routing unit 152 (asis illustrated) for greater fault-isolation.

The routing unit 152 accepts a standard DMX-512 serial input. In a knownmanner, its hardware consults a lookup table that contains the lowestdimmer number addressed by the raceway "blob" on each of its outputs153A-153G. Each of these outlets will remain quiet until the incomingDMX-512 packet reaches the level for the first dimmer number on theraceway section whose "blob" is coupled to that outlet. The routing unitthen passes on only those levels for outlets on that raceway section andthen reroutes the transmission to the next raceway section.

The first byte that raceway "blob" 154A will see from the routing uniton 153A will be the desired intensity byte for the dimmer plugged intooutlet 231A. The raceway "blob" will automatically switch eachsuccessive intensity byte to the next outlet/LED.

Thus, the dimmer plugged into an outlet sees only the intensity byte forthat outlet and no address decoding function is required at the dimmer.

The components at each raceway receptacle are limited to one LED, whichis wired back to a simple, plug-in "blob".

One multi-pair cable connects a raceway with the centralized routingunit. There is no high-speed multi-drop serial communications and a highdegree of fault and electrical isolation is possible.

The routing unit can also suppress transmissions to the modules to turnoff preheat when the console is active (producing DMX out) but no dimmerhas received a level for some defined period.

Variations employing fewer conductors are also possible.

One method is.to matrix the light-emitting diodes at the racewayoutlets. For example, one side of each LED is connected to one of eightdriver lines #1-8 and the other to one of eight return lines #9-16. Eachsuch LED is connected across a unique pair of such lines.

While such an arrangement can be used to drive a single LED at a time,throughput can be increased or the data rate decreased if thedistribution "blob" drives all LEDs on the same return line at the sametime. For example, the first bit is loaded into drivers #1-8 for theLEDs on return line #9, which is then be enabled to simultaneously lightall those LEDs on the return line having data "1". This process isrepeated through all the data bits for those dimmers/outlets on returnline #9, and then advance to those LEDs on return line #10.

This approach effectively decreases the baud rate between the input andoutput side of the "blob" by a factor of eight, which may haveadvantages in terms of the response time of relatively inexpensive cableused to connect the blob with the LEDs, as well as the response time ofless expensive LEDs and photodetectors

The technique of driving multiple LEDs simultaneously can also beemployed with the "discrete pair per LED" approach, but the "matrix"approach reduces the number of signal conductors in the raceway itself,provided that the driver and return lines are run through the racewayand the LEDs are tapped into them at or near their outlets. This can beaccomplished with known insulation-displacement tap connectors such asthe Scotchlok Brand "UB" connector by the TelComm Products Division of3M Corporation.

The "matrixed" approach to wiring has several tradeoffs. Installing thetaps (by whatever means) requires access to (and produces servicepoints) across the length of the raceway. Failure of one driver orreturn line will affect a number of outlets/dimmers and may do so(particularly if intermittent) while producing symptoms that may bedifficult for an end user to interpret correctly. Such conductorsextending long distances parallel to the line voltage conductors of theraceway might be subject to EMI. Shielding such signal conductors ismade more difficult by the requirement for regular taps. Providing aseparate compartment in the raceway for shielding the low-voltage wiringincreases the cost and complexity of raceway construction and presentsthe problem of routing the tap pigtails for the LED through theline-voltage section on the way to the LED mount on or near the powerconnector. The taps may also increase the cross-sectional arearequirements of such a compartment, which decreases the useablecross-sectional area in the line voltage portion of the raceway,reducing the maximum number of line voltage circuits for a given overallraceway envelope under electrical code percentage "fill" restrictions.

Despite these potential tradeoffs, the use of such approaches will besuitable for many applications. The electrical isolation by any knownmeans of driver lines from the connection between the raceway "blob" andthe routing unit permits the presense of both power wiring and thedriver lines in the same compartment, without the requirement for adivider or partition to satisfy electrical code requirements. Shieldingcan be made integral with the driver lines or provided by foil orsimilar tape over them, which may also serve to dress and protect them.Flexible printed circuit material may be used in lieu of discreteconductors.

A generally similar scheme can be used to distribute the undividedserial data stream to each outlet for dimmers and other users withindividual address decoders.

In any of the embodiments disclosed herein, dimmers or other users canbe adapted to recognize either discrete values in a serial data streamon the basis of a local address decoder; a supplementary or temporaryvalue; a "presorted" value; a value for a connected accessory; or an"all users" transmission by the use of different start codes to theserial data stream.

It will further be understood that, either in the context ofindividually-driven or matrixed LEDs, that the "blob" and/or the routingunit, can serve to convert from higher to lower baud rates, and/or toalter the manner in which the desired intensity or other value isexpressed. For example, the "blob" can accept a serial digital input,and convert the information to either pulse-width or frequency-modulatedform. This can permit a marked reduction in the complexity of thereceiving circuitry required in the dimmer. Further, the routing unitand/or "blob" can selectively distribute non-dimmer information tooutlets identified as coupled to, for example, motorized fixturesinstead of just dimmers, and further permits the distribution of unequalquantities of data to different outlets/addresses in the same system,based on the needs of each connected device.

SIGNAL DISTRIBUTION BY RADIANT ENERGY

Another means of serial data transmission a raceway system would placeone or more high-powered emitters such as LEDs or laser diodes so as todirect their output into the interior to the raceway. The emitter wouldthen pump serial data in visible or IR light form into the interiorvolume of the raceway, where reflection from its surfaces and/ordiffusion or light pipe elements fills the interior volume of theraceway with this data, such that dimmer enclosures 609 (or any other"user") can sense it by inserting a photodetector or optical extensionof it in or through a window or hole in the raceway into its interiorvolume. Materials for the construction of dedicated light guides (suchas Scotch brand Optical Lighting Film by 3M Corporation) are alsoavailable.

In some applications, desired intensity values encoded as infrared lightcan be broadcast through free air, or similar wireless means employed.

Another approach is the use of a "fiber optic bus" such as manufacturedby Ensign-Bickford Optics Company (Avon, Conn. 06001). This consists ofa main fiber optic cable to which "taps" have been attached by creatingan aperture in the fiber cladding through which a small quantity oflight can escape, and by fixing a tap fiber (generally using atransparent epoxy) so as to collect the light escaping through thatopening. "Trunk" or main fibers with 60 or more taps have beenfabricated. The main fiber is driven by a suitable LED transmitter and aphotodetector can be coupled to the free end of each such tap.

Such a "fiber optic bus", installed within the raceway and providing atap for every outlet, can distribute data to the outlets at a data ratefar exceeding the requirements of the application. The arrangement isfunctionally inert, immune to the effects of EMI, requires no separatecompartment or shielding, and, if properly fabricated, offersessentially unlimited life.

A single fiber provides a single bus with no provision forselectively-addressing each outlet/dimmer. Therefore the user would haveto manually enter the address on each dimmer/interface module--or aseparate means of automatically addressing the dimmer or interfacemodule would be required. Examples of such means include the use of thepreviously described retro-reflective photosensor array reading abinary-coded bar code label on the outlet or raceway; or miniature barmagnets inset in the outlet housing activating Hall Effect sensors inthe dimmer or interface module.

An alternative is to use multiple fiber optic busses with a modifiedaddressing scheme. In one example, six main fibers are provided, eachwith its own LED driver.

Each raceway outlet provides for two tap fibers and eachdimmer/interface module has two photodetectors, one aligned with eachtap fiber.

Taps are installed along, for example, six main fibers to produce a pairof taps at each of 30 outlet locations. These pairs might be: 1/2, 1/3,1/4, 1/5, 1/6, 2/1, 2/3, 2/4, 2/5, 2/6, 3/1, 3/2, 3/4, 3/5, 3/6, 4/1,4/2, 4/3, 4/5, 4/6, 5/1, 5/2, 5/3, 5/4, 5/6, 6/1, 6/2, 6/3, 6/4, and6/5. (Each combination/pair of main fiber numbers is repeated twice,once with that pair in each possible left/right relationship.)

The two photodetectors in the dimmer or interface module are coupled tologic such that, for example, the left tap is treated as the "enable"input. When that tap is energized "steady on", the module will acceptany data on its right tap as data addressed to it. In the mannergenerally described earlier, the raceway "blob" energizes the driver formain fiber #1 and then transmits the data for the first five addressesusing drivers/cables #2-6. It then proceeds to sequentially "enable"fibers #2-6 and repeat the process with the other five fibers for each"enabled" one.

Alternatively, the system can omit the "enable" function and simplyExclusive-AND the output of the two photodetectors such that adimmer/module will only accept data sent on both of the lines to whichit has been tapped. This, however, reduces both the number of outletsthat can be addressed by a given number of main cables, and makes itimpractical to address multiple outlets simultaneously. While theExclusive-OR approach permits transmitting to all addressessimultaneously by simply sending on all lines, a similar function can beproduced on the modified system by sending a number of messages equal tothe number of lines (and not outlets).

The number of main fibers can be increased or decreased depending uponthe number of outlets to be addressed. The tap system can also be usedin reverse such that multiple nodes can drive a common main fiber. Thismight take the form of a single main fiber with taps for each outlet.

The disclosed selective addressing scheme can also be used with a wireddistribution scheme.

The LEDs or fiber optic taps used by any of these schemes can be insetdirectly into the power connector as a method of reducing thefabrication cost of the raceway and of assuring physical registration ofthe emitter and detector.

Refer now to FIGS. 5K and 5J. A combined power and signal connector 232has been produced by enlarging the die for a standard "pop-in" pinconnector receptacle such as the previously-described Harj-Lokreceptacle made by Union Pin Connector Company, Inc..

The enlarged connector provides not only contacts 213H for "hot", 213Nfor neutral, and 213G for ground, but a fourth contact 213R that permitsthe plug-in dimmer module to return its output to the raceway for supplyto a pigtail or receptacle mounted on the raceway rather than on thedimmer module itself, as has been previously described. The enlargedconnector also provides two wells for the insertion of suitablelight-emitting diodes. A standard solderless LED connector 232R such asthe Conxriter unit by Visual Communications Company, Inc. (San Diego,Calif. 92126) (which also incorporates an internal resistor) may beinserted in each of two wells 232W provided in the connector body 232B.The LED connector 232R has contacts to which wire leads 232L can besoldered. These contacts can also accept known quick-connect terminals232T, which are plugged in place. A reduction in the size of the passhole through the bottom cap 232C of the connector 232C prevents strainon the flying leads 232L from unplugging terminals 232T from thecontacts of LED connector 232R.

A suitable visible or IR LED is plugged into each of the LEDreceptacles. An LED 232S is shown plugged into the LED receptacleadjacent power contact 213N.

The two LEDs in each dimmer receptacle 232 therefore result in fourflying leads, and such LEDs may be wired in any of the previouslydescribed methods.

It will be understood that in cases where the power connector is mountedatop the raceway, that an LED or fiber optic port may be mounted on theside of the raceway to prevent the natural accumulation of dust fromattenuating output.

It will further be understood that other contact and non-contact methods(for example, inductive coupling) may be used to couple controlinformation between the raceway and the dimmer or other user.

It will be understood that, in addition to dimmer enclosures such asillustrated in FIG. 6A-6M, that the use of non-contact coupling of thecontrol signal may employ an adaptor, plugging into the raceway, andserving the function of converting the encoded control signal into anelectrical signal that can be coupled via a suitable connector and cable(or amplified to drive a fiber-optic link) to a remotely locatedfixture.

While the various schemes for distributing control information aredescribed in the context of a raceway system employing the distributeddimmer disclosed, it will be apparent that the above techniques can beapplied individually or in combination to other distributable packagesand to dimmer racks and dimmers of conventional construction. PhysicalEmbodiment of FIG. 7A and 7B

In some cases, an elongated raceway or portable enclosure may not bepractical, such as at some exposed locations in the auditorium itself.

Refer to FIG.7A and 7B, where a fourth mechanical embodiment isillustrated.

The illustrated embodiment employs cast or extruded modules such as760C, that incorporate at least the semiconductor power devices. In amanner generally analogous to the embodiment of FIG.6D and 6E, themodule is provided with a male inlet connector and an additionalconnector or pole for returning the dimmed output. In the case of theinstant embodiment, such connectors are mounted to the metal cover plate780 mounted on a flush or surface mounted backbox by means of mountingholes 781. The panel is further illustrated as mounting circuit breakers775, such that the panel may be supplied with a single, relatively largeservice (e.g. 60A) and itself provide the branch circuit protectionrequired by electrical code for a plurality of smaller capacity dimmers.The illustrated module provides a well that protects and encloses thehandle of circuit breaker 775, that well further provided with a web 765that extends under the breaker handle in the "on" position, such thatthe module cannot be inserted or removed without the breaker handlebeing turned off. Panel 780 mounts power outlets 211 that permit theuser to plug directly into the panel for "hot-pockets", as well asreturn receptacle 211R that is connected to a remotely located lampload. .Control signals are coupled to the electronics on the module viaa contact or LED at 232S. The module is aligned with the plate 780 bymeans of a latch 772 and pin engaging holes 773 and 774 respectively.Other means may be provided, and the functions of the power inlet, powerreturn, and control signal connectors may be combined as previouslydescribed and illustrated. The power outlet connector may also bemounted on the module. Similarly, the use of a standard Edisonparallel-blade connector 769 for module 760B is shown, illustrating thatsuch Edison connectors (or corresponding English or European powerconnectors) can also be employed for this or the previous embodiments.

PHYSICAL EMBODIMENT OF FIG. 8A-8F

Finally, while distributed dimmer systems packaging dimmers for use witha lamp support and on regular mounting centers are practical for certaintypes of touring systems, they are not as practical for many touringtheatrical productions, that vary the number and mounting centers offixtures per mounting position as well as the arrangement of fixtures atthe mounting position itself.

A theatrical production may, for example, hang fixtures on 18" centerson one pipe and on 24" centers on another, while requiring clumps ofthree circuits at borderlight pigtails. The production may pack one pipewith fixtures, while using less than a half-dozen on another; sidearm asingle vertical row of fixtures on the downstage boom and a double rowin the boxes

It will be apparent that, on one hand, a system of dimmers on fixedmounting centers and/or in an elongated housing is impractical for manyof these variations, while a system of single dimmer enclosures asillustrated in FIG. 3A-4C requires an undesirably large number ofdiscrete supply cables and connections.

Refer now to FIG. 8A-8D where a fifth mechanical embodiment isillustrated that provides a single enclosure design equally suited toeach such variation.

FIG. 8A is a plan view of the embodiment. FIG. 8B is a front elevation.FIG. 8C is a plan view illustrating one application of the embodimentFIG. 8D is a front elevation of FIG. 8C.

Enclosure 809 contains three discrete power stages, supplyingreceptacles 211A, 211B, and 211C respectively. Male multi-polemulti-connector 753 supplies both signal and three-phase 120/208 voltpower, to which both the dimmers and a female multi-pole receptacle 752are parallelled, the latter so that additional enclosures may be"daisy-chained" to the same cable (e.g. enclosures 809 and 809A bothsupplied by cable 755). One power stage is connected to each of thethree phases.

Many designs for enclosure 809 are possible, and should not beunderstood as limited except by the claims. Heat sink fins 817 or "pinfins" 818 may be provided, and a common chassis used for all three powerstages, or each power stage packaged on a removable submodule (e.g.819).

The embodiment illustrated employs a single membrane switch panel 820,as manufactured by the Xymox Division of W. H. Brady Co., Milwaukee,Wisconsin 53201, which provides test buttons such as 320 and transparentportions for signal and power indicators such as 318 and 320, which maymount to a printed circuit card beneath it. The function of addressthumbwheel switch 315 in the previous Figures is performed by thecombination of an up/down counter responsive to up/down buttons 816 anddisplay 815, a two-digit 7-segment LED array. To prevent accidentalchanges in address, a "set" button 817 is provided which must bedepressed to enable up/down buttons 816.

Referring now to FIG. 8C and 8D, enclosure 809 may be mounted to a pipe(or any similar support) using a clamp 859. In contrast to the boxyenclosures which have previously been disclosed, the improved dimmer ofthe present invention can be installed in an enclosure of minimal size,whose elongated shape minimizes obstructions and locates receptacles211A-211C such that all three fixtures supplied by the enclosure (e.g.,301A, 301B, and 301C) may be plugged into the receptacles without therequirement for an extension cable. Further, adjusting the distancebetween two enclosures (e.g., 809 and 809A), allows adapting to avariety of fixture mounting centers.

While inlet multi-connector 753 could be panel-mounted, it is preferablyinstalled at the end of a pigtail comprising a length of flexibleconduit 863 containing the required power and signal conductors 861,attached to enclosure 809 via hub 865. Plugging the male inlet connector753 of one enclosure (e.g., 809A) into the female receptacle 752 of asecond enclosure (e.g., 809) connects the two without the requirementfor a separate jumper and automatically spaces the two enclosures by thedistance required to accomodate the regular mounting centers of fixtures301A-301E. It will be apparent that the combination of the enclosures ofFIG. 8A-8D with multi-conductor and conventional stage pin connectorequipped cables, provides a uniquely efficient method of dimmingfixtures on pipes and similar elongated supports, whether packedtogether on regular centers or widely and irregularly spaced apart.

It will further be apparent that a single such enclosure can be locatedon the ground or in the air wherever a borderstrip or cyclorama lightrequires three circuits, and that the same enclosure, orientedvertically, singly or in pairs, is equally applicable to booms andsimilar vertical positions.

The use of a plug-through design permits most efficient use of a cable,as any number of enclosures can be "daisy-chained" to the maximumcapacity of the supply cable 755. Thus, given a supply cable rated at 20Amperes, one enclosure can control three 20A loads, two enclosures cancontrol six 1000-watt fixtures, and a third enclosure can be added when750-watt fixtures are employed.

The use of three-phase power makes most efficient use of the cable byminimizing the number of conductors required, while employing threepower stages per enclosure evenly distributes the load--and provides themaximum number of outputs which a single enclosure can supply to almostany arrangement of fixtures without the requirement for extensioncables.

The illustrated embodiment offers a heretofore unattained combination ofbenefits. In contrast to present professional practice which requiresthe time consuming preparation of single or multiple circuit cables ofthe correct length, carefully identified with the required circuitnumber, and the use of large, heavy, and expensive dimmer racks in acentral location; a user of a dimming system of the illustratedembodiment present invention need do little more than circle triplets offixtures on the light plot and order a corresponding number ofenclosures, along with an assortment of cables. At the load-in,enclosures are simply clamped to the mounting positions and theiraddresses set, then connected with one or more portable circuit breakerpanels located for maximum convenience, using multi-conductor cableswhich need not even be identified. The resulting system not onlyrequires less labor to prepare and install, but less capital to build,due to the dramatically less expensive cable and multi-connectors whichcan be employed as well as the savings produced by the replacement ofthe large and mechanically complex racks.

The same cables can be used to supply motorized and automated fixtures,which may be "daisy-chained" in series with dimmer enclosures. Byrotating the phase conductors between the inlet and outlet connectors ofsuch a fixture, the load presented by multiple such fixtures on a commonmulticable can be equalized.

FIG. 8E and 8F illustrate variations designed to nest over the pipe 127from which the fixtures are hung. Because such enclosures must fitbetween the clamps used for the fixtures, the length of the enclosuresshould be reduced below the minimum fixture mounting centers expected.Both variations also employ forced-air cooling, by means of miniaturefan 817D, which draws air through opening 817D and pressurizes theinterior volume of the enclosure. The enclosure further includes heatsink fins 817F thermally-coupled to the surface mounting semiconductorpower device 519E or 519F. Thermal losses from the devices are radiatedto free air from the external surfaces of the enclosure, while thepassage of air through the interior volume of the enclosure and throughthe heat sink 817F and out outlet 817G improves heat transfer.

Enclosures 809B and 809C may be retained on pipe 127 by a mechanicalclamp and/or a magnet.

The preferred embodiments disclosed are intended for purposes ofillustration, and it will be apparent to those of skill in the art thatother variations, combinations, and embodiments are possible within thespirit and scope of the inventions.

The triggering circuits may be located remotely from the power stage.

Parallel, serial, or wireless transmission (including power line,infrared, or ultrasonic) of control signals may be employed.

Signal and power conductors for any of the embodiments may be combinedin common cable and/or connector assemblies, or separate cables/and orconnector assemblies may be employed.

The power stage, triggering, and/or transition control means may beintegrated in a single semiconductor package.

While the preferred embodiment illustrated is for a power stage havingan AC output, it will be understood in the context of U.S. Pat. No.4,438,356 that rectification could be employed such that the output ofthe power stage would be DC. Such an arrangement would further reduceaudible lamp noise, while its use in a distributed applicationeliminates the requirement for DC rated connectors and two-wireoperation except at the fixture, while simplifying the operation ofarc-detection circuitry, if employed.

The combination of rectification with a filter capacitor and voltagefeedback would offer the further prospect of compensating for voltagedrop to maintain full RMS voltage at the lamp.

Other variations may be made without departing from the spirit of theinvention, which should not be understood as limited except by theclaims.

What is claimed is:
 1. An electronic dimming apparatuscomprising:semiconductor power controlling means for selectivelycoupling a lamp load with an alternating current supply; means, havingan output coupled to said semiconductor power controlling means, forvarying the amount of power supplied to said lamp load over a range ofpower by controlling the fraction of a half-cycle of the waveform ofsaid alternating current supply in which said semiconductor powercontrolling means couples said lamp load with said alternating currentsupply, said means for varying having:an input for a first value, saidfirst value indicative of a desired amount of power to be supplied tosaid lamp load; digital means for substituting a second value for saidfirst value; means for inputting a third value indicative of the actualamount of power supplied to said lamp load; and means, responsive to atleast said second value and said third value and operatively coupledwith said output, for adjusting said fraction so as to minimize adifference between said desired and said actual amounts of power.
 2. Theapparatus according to claim 1, wherein said means for varyingstabilizes the RMS voltage supplied to said lamp load for a given saidfirst value.
 3. The apparatus according to claim 1, wherein said meansfor varying permits selecting one of a plurality of differentrelationships over said range between said first value and said secondvalue, such that one of a plurality of different relationships over saidrange between said first value and said actual amount of power isselected.
 4. The apparatus according to claim 3, wherein said selectionis afforded by a plurality of stored sets of second values.
 5. Anelectronic dimming apparatus, comprising:a semiconductor powercontrolling means having a control input and coupled with a power inputfrom an alternating current supply and a power output suitable forcoupling to a lamp load, said semiconductor power controlling meansadapted to vary the instantaneous amplitude of the voltage or currentsupplied to said lamp load between at least a substantially conductiveand a substantially non-conductive power condition; means for triggeringhaving an output coupled to said control input of said semiconductorpower controlling means, said means for triggering variably controllingthe average power supplied to said lamp load over a range of power byvarying the phase angle of a half-cycle of the alternating currentwaveform at which said semiconductor power controlling means changesfrom one of said power conditions to the other one of said powerconditions, said means for triggering having an input and responsive toa value at said input indicative of a desired amount of power to besupplied to said lamp load, said means for triggering providing analognegative feedback having high loop gain across substantially the entiresaid range of variability of power comparing the actual amount of powersupplied to said lamp load with said desired amount of power todetermine any difference and altering said phase angle so that saidactual amount tends toward said desired amount; said means fortriggering digitally substituting a compensated value for said inputvalue; and said feedback being responsive to said compensated value. 6.The apparatus according to claim 5, whereina means is provided for thedistribution of at least said alternating current supply to said powerinput; a mechanical interface is located between said dimming apparatusand said means for distribution; electrical isolation is providedbetween said dimming apparatus and a source of said value indicative ofa desired amount of power by a separable coupling across said mechanicalinterface and prior to said means for triggering.
 7. A method ofcontrolling the phase angle at which a lamp dimmer having an inputchanges the conductive condition of a semiconductor power controllingmeans to provide a lamp load with a desired amount of average powerwithin a range of possible average power amounts, comprising the stepsof:inputting a first value via said input, said first value identifyingan amount of average power desired for said lamp load; providing saidlamp load with power; inputting a second value indicative of the actualamount of power supplied to said lamp load; digitally deriving from saidfirst value a third value; employing analog feedback having a high loopgain comparing said third value and said second value to determine anydifference between said actual and said desired amounts of power;altering said phase angle so as to minimize said difference.
 8. Themethod according to claim 7, wherein the relationship between said firstvalue identifying a level of desired average power and a correspondingthird value substantially compensated for the effects of said high loopgain.
 9. Lighting control apparatus comprising:a substantially rigidhousing; at least one enclosure engaging said housing, said enclosurecontaining at least one dimmer; said dimmer including a semiconductorpower controlling means and a means for triggering, said semiconductorpower controlling means coupled with a power input from an alternatingcurrent supply and a power output suitable for coupling to a lamp load,said means for triggering variably controlling the average powersupplied to said lamp load over a range of power by adjusting therelative proportion of a half-cycle of the alternating current waveformin which said semiconductor power controlling means is in asubstantially conductive versus a substantially non-conductive powercondition; said means for triggering having a first signal input andresponsive to at least one value received at said first signal input asindicative of a desired level of average power to be supplied to saidlamp load; said housing distributing to said dimmer in said enclosure atleast said alternating current supply and said value; said alternatingcurrent supply being coupled between said housing and said enclosure bymating power contacts; and said value being coupled between said housingand said first signal input of said at least one dimmer in saidenclosure via a separable electrically isolating coupling.
 10. Theapparatus according to claim 9, wherein said separable electricallyisolating coupling comprises at least one effective source carried bysaid housing and at least one detector carried by said enclosure. 11.The apparatus according to claim 10, wherein said source emits light.12. The apparatus according to claim 9, wherein signals modifyingparameters of the light output of said lamp load in addition tointensity are coupled via said coupling.
 13. The apparatus according toclaim 9, wherein there are a plurality of said enclosures, each engagingsaid housing.
 14. The apparatus according to claim 13, wherein saidseparable electrically isolating coupling comprising at least onedetector carried by each of said enclosures and at least one source;saidsource having an output common to said detectors of a number of saidenclosures.
 15. The apparatus according to claim 14, wherein theinternal volume of said housing conveys said output of said commonsource to said detectors of said number of said enclosures.
 16. Theapparatus according to claim 14, wherein said source emits light. 17.The apparatus according to claim 16, wherein a material conducting lightconveys said output of said source to said detectors.
 18. Lightingcontrol apparatus comprising:a substantially rigid housing; a pluralityof enclosures engaging said housing, each of said enclosures containingat least one dimmer; said dimmer including a semiconductor powercontrolling means and a means for triggering, said semiconductor powercontrolling means coupled with a power input from an alternating currentsupply and a power output suitable for coupling to a lamp load, saidmeans for triggering variably controlling the average power supplied tosaid lamp load over a range of power by adjusting the relativeproportion of a half-cycle of the alternating current waveform in whichsaid semiconductor power controlling means is in a substantiallyconductive versus a substantially non-conductive power condition; saidmeans for triggering having a first signal input and responsive to atleast one value received at said first signal input as indicative of adesired level of average power to be supplied to said lamp load; saidhousing distributing to said dimmer in each said enclosure at least saidalternating current supply and said value; said alternating currentsupply being coupled between said housing and each said enclosure bymating power contacts; and said value being coupled between said housingand said first signal input of said at least one dimmer in each saidenclosure via a separable electrically isolating coupling.
 19. Theapparatus according to claim 18, whereinsaid separable electricallyisolating coupling comprises at least one detector carried by each ofsaid enclosures and at least one source; and said source having anoutput common to said detectors of a number of said enclosures.
 20. Theapparatus according to claim 19, wherein the internal volume of saidhousing conveys said output of said common source to said detectors ofsaid number of said enclosures.
 21. The apparatus according to claim 19,whereinsaid source emits light; and a medium conducting light conveyssaid output of said source to said detectors;
 22. The apparatusaccording to claim 21, wherein said source and said power contacts arecombined in a common mechanical assembly.
 23. The apparatus according toclaim 22, wherein said common mechanical assembly is suitable forinsertion in said housing.
 24. The apparatus according to claim 18,wherein signals modifying parameters of the light output of said lampload in addition to intensity are coupled via said coupling.